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Femoral trochlear dysplasia: MR findings
C W Pfirrmann1, M Zanetti, J Romero
1Department of Radiology, Orthopaedic University Hospital, Zurich, Switzerland. pfirrm16@centralnet.ch
Purpose:
To establish quantitative and qualitative magnetic resonance (MR) criteria for the diagnosis of trochlear dysplasia.
Materials And Methods:
MR images were analyzed in 16 consecutive patients with and 23 without trochlear dysplasia. The standard of reference was a true lateral radiograph of the knee. Quantitative and qualitative MR criteria were assessed.
Results:
In patients with trochlear dysplasia, the trochlear groove was significantly less deep than that in control subjects. The most accurate measurement was 3 cm above the femorotibial joint space (P: <.001), where a trochlear depth of 3 mm or less had a sensitivity of 100% and a specificity of 96%. The ventral trochlear prominence between the supratrochlear femoral cortex and the most ventral point of the trochlear floor (midsagittal section) was always larger than 6.9 mm in dysplastic trochleae. A facet ratio of less than 2:5 (medial to lateral) 3 cm above joint space level had a sensitivity of 100% and a specificity of 96%. A nipplelike anterior prominence at the superior end of the femoral trochlea on midsagittal images was a specific (91%) qualitative criterion.
Conclusion:
Dysplasia of the femoral trochlea can be diagnosed reliably by using quantitative or qualitative criteria on midsagittal or transverse MR images obtained 3 cm above the femorotibial joint space.